Phenotype switch and activation of T lymphocytes in patients with allergic rhinitis

The peripheral blood of 17 patients with seasonal allergic rhinitis (birch pollen) and of 10 healthy subjects were analysed before and during a provocation study in the non-pollen season as well as during the pollen season. Analytical flow cytometry comprised a panel of monoclonal antibodies investigating helper/suppressor T cells, activated T cells, and naive/memory T helper cells. Allergic patients showed no increase in the amount of T lymphocytes but an increased proportion of CD4+ helper T cells early during pronounced exposure (provocation) but not during natural antigen exposure (pollen season). Allergic patients showed a significant increase in activated T cells during the non-pollen season compared with healthy subjects, and furthermore, the nasal allergen provocation induced an additional increase in activated T cells among allergics. The T cell activation mainly affected helper T cells (85%) rather than suppressor T cells. Furthermore, allergic patients showed a significant increase in naive T helper cells during the pollen season. The presence of a double-positive subpopulation indicates an activated T helper subpopulation that switches its phenotype from naive (CD45RA) to memory (CD29). The results indicate at least two important differences between patients with allergic rhinitis and healthy controls. In allergic patients T helper cells become activated upon allergen exposure, and circulate in the blood and switch their phenotype. These T cells have a potential homing tendency to the nasal mucosa. These two events do not occur in non-allergic individuals and may thus constitute new insights into the basic mechanisms of allergic rhinitis.